Two Approaches for advanced presence services in SIP communications

This paper presents the comparison and analysis of two approaches for providing advanced presence services in session initiation protocol (SIP) standard. One approach is investigated by the strategy group at Mitel networks, which allows a watcher to know the availability of a presentity whose subscription policies and notification policies are written in presence and availability policy language (PAPL). The other approach is proposed by our group at University of Ottawa, which delivers a presentity\´s status with rich information to its watchers. The extended call processing language (CPL) is used to describe presence-processing policies. Besides the well-known "online" and "offline" presence indicators, the two approaches use a much broader presence information, which includes "location" "time" and "role" etc., to provide much advanced presence services and personalized services. Personalized services are provided based on a person\´s role, address, time, location, or any of their combinations.